The invention described herein is a pipeline pig that provides a method of applying a treating fluid, such as an inhibitor or a cleaning chemical, within a pipeline to specific longitudinal and circumferential areas along the inner wall of the pipeline and particularly to the upper interior portions of the interior wall of a pipeline. Pipelines, particularly those designed to carry large volumes of gas under pressure, are customarily made of metal and usually of steel. Steel is the preferred metal for construction of a pipeline due to its inherent strength, availability, and economy. However, steel is subject to corrosion as a consequence of oxidation or reaction with gasses or liquids, such as water, that is commonly encountered when large volumes of gas are delivered through a pipeline.
To combat corrosion, a standard technique employed by many operators of pipelines is to periodically deposit inhibitor liquid within the pipeline. The liquid can be moved by the flow of gas through the pipeline or more commonly, by the use of pipeline pigs inserted into the pipeline and moved by the flow of gas. The pigs serve to provide a moving plunger within the pipeline that tends to sweep liquid within the pipeline before it and to therefore move the liquid through the full length of the pipeline. One method of applying a treating liquid to the interior of a pipeline is called “batching” in which treating liquid is captured between two pipeline pigs that move in tandem. Although this method is widely accepted and used it does not insure that the upper quadrant of the interior of a pipeline is adequately coated with or exposed to the treating liquid.
A second method of treating the interior cylindrical surface of a pipeline is called the “injection method.” In this method, the treating liquid is injected directly into the pipeline and is moved by gas flow to carry the liquid through the length of the pipeline. This method is costly and usually requires that treating liquids be more or less continuously injected into the pipeline. There is no direct application, in this method, of the treating liquid to the inner wall because liquid simply condensates and rests on the bottom interior surface of the pipeline.
A third method of treating the interior cylindrical surface of a pipeline is called the “dispersion method,” and is disclosed in my U.S. Pat. No. 6,874,193. In this method, a pipeline pig is positioned in a pipeline that has a treating fluid, and the pig is moved by gas flow through the pipeline. The pig is configured to move liquid forward in advance of the pig so that the liquid will be carried from one area to another within the pipeline. As the pig moves through the pipeline and pushes liquid along ahead of it, some of the pressurized gas from the rearward end of the pipeline pig flows through a rearward inlet, through the interior of the pig body, and out through a bypass passageway. The rearward inlet is preferably placed close to the interior bottom of the pipeline. The gas flow surrounds a siphon passageway and draws liquid within the lower interior portion of the pipeline into an inlet end of the siphon passageway. The application of a reduced pressure at the outer end of the siphon passageway draws liquid from within this siphon passageway and carries it with the gas so that a spray of liquid is formed and ejected from a nozzle opening to cover an upper interior segment of the pipeline interior cylindrical wall.
The shortcomings of the current dispersion method are (1) a large volume of bypass gas or liquid cannot flow through the pig body or nozzle, (2) discharge velocity and the mixing effect of the nozzle are limited by differential pressure, and (3) a plurality of nozzles is required in order to achieve direct top coating application. Therefore, there is a need for a dispersal apparatus that addresses these shortcomings and provides for improved dispersion and coating effect.